The present invention relates generally to methods and apparatus for fixing dye to pile fabrics such as carpet material, a process commonly known as steaming. More particularly, the invention relates to methods and apparatus employing the electrical conductivity of the wet carpet itself for the purpose of heating the carpet and dye to a temperature sufficient to fix the dye.
Carpet dyeing processes require at least two steps, done in sequence: (1) applying dye in liquid form to the carpet; and (2) fixing the dye to the carpet. It will be appreciated that "liquid form" is a general term, and includes foam, mist, and spray. Once the dye is fixed (or set) it becomes a stable and an essentially permanent part of the carpet fiber material.
Nearly universal conventional practice for fixing dye to carpet is to employ a steam chamber or oven, usually termed quite simply a "steamer". While known steamers take a variety of forms, typically they comprise an elongated chamber through which a web or length of carpet passes following dye application. In order to confine the steam with a minimum of loss, the elongated chamber is enclosed with slot-like openings at the entrance and egress for the carpet to pass through. Steam may be introduced either through a plurality of nozzles, a vat of boiling water below the path of the carpet, or a combination of both. The carpet may either pass straight through the steamer, or, by employing suitable guide rollers, may be guided in a serpentine path. Within the steamer, the carpet and dye are heated substantially uniformly to a sufficient temperature, with the presence of sufficient moisture, to cause fixation of the dye material to the carpet pile or nap. Generally, the boiling temperature of water at normal atmospheric pressure, i.e., 100.degree. C., is sufficient for this purpose, although it may be noted that in some steamers a slightly higher pressure and thus temperature are employed. Following the steamer, the carpet is dried.
It will be appreciated, as is well known in the field of carpet dyeing, that, while dye fixation is a necessary step, a conventional carpet steamer is quite costly in a number of respects. One significant cost of operation is in energy inasmuch as a relatively large quantity of water must be heated to its boiling point temperature and, moreover, as a practical matter must be maintained at such temperature even during standby periods when carpet is not being run through the machine in order that the machine will be ready for each succeeding length of carpet. Adding to the cost of operation is the fact that a certain portion of the steam is necessarily lost to the process as a result of leakage, and thus never contributes to any useful purpose.
A conventional carpet steamer is also relatively expensive in terms of capital cost, both for the equipment itself and for the floor space required. Conventional steamers are typically one hundred fifty feet long, and thus use substantial amounts of floor space.
Despite these drawbacks, such steamers have long been conventional practice, which evidences the lack of any practical and acceptable alternative.
One alternative which has been proposed, although not specifically for carpet, is the use of microwave energy for fixing dyes to dyed textile materials. Such an approach is disclosed in Kawaguchi Pat. Nos. 4,274,209 and 4,365,422. Nevertheless, conventional steamers as summarized above have remained the standard for carpet dyeing purposes.
In the context of the present invention, it is pertinent to note that heating by electrical conductivity has been proposed for a variety of purposes. For example, U.S. Pat. Nos. 1,624,029 to Whitcomb, Tompkins 1,626,766, Malachek 2,824,383, Christgau 3,000,106 and Lippke 3,057,075 propose various apparatuses for heating and thus drying paper by electrical conductivity. The Malachek Pat. No. 2,824,383 also proposes the drying by electrical conductivity of various other types of wet porous sheets, such as leather, fabric and wood. None of these patents, however, suggest the use of electrical conductivity for fixing dye to carpet.